Drinking flask



FIG. 1 is a front elevation view of a drinking flask showing our new design;

FIG. 2 is a rear elevation view of the drinking flask of FIG. 1;

FIG. 3 is a left side elevation view of the drinking flask of FIG. 1;

FIG. 4 is a right side elevation view of the drinking flask of FIG. 1;

FIG. 5 is a top view of the drinking flask of FIG. 1;

FIG. 6 is a bottom view of the drinking flask of FIG. 1; and,

FIG. 7 is a top perspective view of the drinking flask of FIG. 1.

The broken lines represent portions of the drinking flask that form no part of the claimed design. 

CLAIM The ornamental design for a drinking flask, as shown and described. 